I. Field of the Invention
This invention relates to apparatus for continuously mixing sand and binders for a foundry. The apparatus comprises a mixing tube having a substantially vertical axis in which laminar blades are mounted for rotation and blend sand and binders fed from above. In such a so-called turbo-mixer the sand is fed to an atomiser formed by a grooved rotor which atomizes and projects the binders to strike, with a centrifugal movement, the grains of sand falling, and those which might be re-projected upwards by the blades.
The descent of the sand and binders, being relatively rapid, is dependent upon the surmounting of each end of all of the blades which exert substantially on all the particles of sand covered with binder an action which renders homogeneous the distribution of the binder on the particles. The blades extend over the entire internal area of the tube. This means that the blades are obliged to cooperate with the internal surface of the tube.
II. Description of the Prior Art
In the present state of the art, devices for continuously mixing sand and binders for a foundry are known in which the mixing takes place in a device having the form of a turbo-mixer. In these devices of known type it has already been realized that the effectiveness of mixing depends on regulation of the flow of the material or else on the time that the material itself takes to traverse the turbo-mixer and for this blades have been made which extend substantially tranversal of the mixing tube, adapting the surfaces thereof destined to receive the falling material so as to produce a rebound of the grains of sand upwards and thus to retard the descent of the material. These blades having an extension substantially transverse to the axis of the turbo-mixer, while indeed bringing about a slowing down of the material being mixed, were not optimum with regard to the effectiveness of the mixing, that is to say the ratio delay/effectiveness of mixing was too high. Also in these turbo-mixers, the effectiveness of the mixing was limited because the surfaces destined for this were of limited area. As for the adherence which is necessary to produce the so-called spatulating effect, this had been obtained by forming the body of the turbo-mixer totally or partially of elastic deformable material. This had the defect that the deformations of the container or body of the turbo-mixer were produced by a very limited number of blades and therefore only those blades were producing effective deformations; the others did not produce the deformation but underwent it and therefore did not develop any effectiveness, but even left channels of free passage which accelerated the advance of the material instead of holding it back to homogenize the mixture.